Birds of Barandabhar Corridor Forest , Chitwan , Nepal

Long term monitoring of bird species was conducted in Barandabhar Corridor Forest, one of the important bird areas of Nepal (IBA). Bird species were identified by the point count method in transect surveys in two-time frames from 2002–2012 and 2015–2016 to obtain the bird species list. We compared our bird list with previously published (after 2000) checklists and compiled the updated checklist of birds of Barandabhar Corridor Forest. We documented 372 bird species belonging to 80 families in Barandabhar, including five Critically Endangered, three Endangered, eight Vulnerable, and 15 Near Threatened species. The Accipitridae family included the highest number of species (n= 32), followed by Muscicapidae (n= 30) and Anatidae (n= 18). Approximately, half of the total confirmed bird species were insectivorous. The list included 63% resident, 27% winter migratory, 7.5% summer migratory, and 2.9% passage migrant species. According to the habitat type, there were 181 species of forest, 74 species of wetland, 24 species of grassland, 70 species of open field, and 23 species of partially wetland birds. This updated checklist of bird species will serve as a reference guide for bird watchers, biodiversity researchers, and support managers for conservation effort; and can be used to track any changes in the composition of bird species in the future.


INTRODUCTION
Nepal is a biodiversity hotspot supporting 9.5% of the world's bird species, i.e., 886 species (DNPWC & BCN 2019). Birds are one of the most studied groups in Nepal, and information on birds is well documented in the form of field guides and reference books (Inskipp et al. 2013). The status and distribution of birds in Nepal has been studied by various researchers (e.g., Fleming et al. 1976;Inskipp & Inskipp 1985;Cocker & Inskipp 1988;Inskipp & Inskipp 1991;Baral et al. 1996;Baral & Inskipp 2004;Inskipp & Inskipp 2012;Baral et al. 2012;Grimmett et al. 2016;Inskipp et al. 2017). In Nepal, wetland birds are the only vertebrate taxon that have been monitored every year since 1987. This survey has gained attention as the mid-winter water bird count (Baral 2009). Such long-term studies on birds and their associated habitats have become pivotal in the designation of Important Bird and Biodiversity Areas (IBAs) in Nepal. Nepal now has 32 IBAs listed (27 declared and 5 proposed with IBA codes) (BCN 2020). One of these IBAs is the Barandabhar Corridor Forest (BCF), which is important for bird conservation. Beeshazar and adjacent lakes are located to the south of the BCF and were designated as a Ramsar Site (Site no. 1313) in 2003.
The global loss of biodiversity is continuing at an alarming rate and increasing anthropogenic impacts are exacerbating the trend of species loss. Despite a significant increase in conservation activities, the rate of loss of species has not decreased (Butchart 2010;Schrauth & Wink 2018). In addition, there are staggering losses of birds in the world (Dirzo 2014;Hallmann et al. 2017;Rosenberg 2019). To monitor and document environmental health and ecosystem integrity such as food availability, birds act as indicator species because they are easy to detect and observe, widely distributed, cover different levels of ecological pyramids, and the links among bird communities, vegetal associations and territory have been clearly demonstrated (Petty & Avery 1990;Padoa-Schioppa et al. 2006;Schrauth & Wink 2018;Rosenberg 2019). Hence, it is necessary for longterm monitoring and to keep baseline records of bird species. The previous studies by Adhikari et al. (2000Adhikari et al. ( , 2018 of birds and wetland birds in BCF were of short duration and have missed many bird species.
BCF, representing the IBA, lacks an updated checklist prepared from long-term monitoring of birds. Our study attempted to fill the gap of previous studies by providing the most recent data with revised nomenclature, vernacular names for public awareness including longterm data from 2002-2012 and 2015-2016 along with a checklist of birds of BCF from other studies after 2000. This checklist will serve as a reference for researchers, conservationists, planners, and bird enthusiasts.

Study Area
Barandabhar Corridor Forest (BCF) covers 87.9 km 2 areas in the north of Chitwan National Park (CNP). It is the only remaining forest patch in Nepal that connects CNP with the Mahabharat range in the north (Bhattarai & Basnet 2004;Lamichhane et al. 2018). BCF has a subtropical climate with winter, spring, and monsoon seasons (Bhattarai 2003). The area of BCF is dominated by Sal Shorea robusta forest and partly by riverine and mixed hardwood forest (Bhattarai 2003;NTNC 2003). This forest acts as a migratory route for different bird species (Adhikari et al. 2000(Adhikari et al. , 2018. The East-West highway (Mahendra Highway) bisects this corridor. The southern part falls under the buffer zone of Chitwan National Park and is guarded by the Nepali army (Lamichhane et al. 2018). Human disturbance is relatively low in the southern part. The northern part falls under the jurisdiction of the Divisional Forest Office, Chitwan and is managed as a protected forest. Despite its legal status of protected forest, human pressure in this part is relatively high due to the dependence of local communities on forest resources such as fodder, fuelwood, timber, grazing, NTFPs, and lack of strong enforcement. BCF is surrounded by heavily populated settlements of municipalities, namely, Ratnanagar Municipality on the east, Kalika on the north-east, and Bharatpur metropolitan city in the west (Figure 1). This has added human-pressure to this corridor and timely consideration for the conservation and management of BCF is needed.

METHODS
Bird species present in BCF were assessed by recording direct sightings. The survey was conducted by a team of experts and field staff of the National Trust for Nature Conservation (NTNC) in two-time frames: 2002-2012 and 2015-2016. NTNC in collaboration with the Divisional Forest Office and Chitwan National Park Office administered both surveys by mobilizing field technicians and researchers. Six survey routes of length ~6 to 11 km were set for the bird survey from 2002 to 2012. For 2015 to 2016, the number of transects were increased to 16 with a length of ~4 to 8 km and changed the orientation of the transects to a cross-section of the corridor (Figure 1). The transects were designed Journal of Threatened Taxa | www.threatenedtaxa.org | 26 September 2021 | 13(11): 19509-19526 19511 J TT (Adhikari et al. 2000(Adhikari et al. , 2018 to prepare the updated bird checklist. We only included bird records after 2000.

RESULTS
BCF was found to support 372 bird species belonging to 20 orders and 80 families (Annexe 1) with a total survey effort of 1,506 km. A total of 287 species was recorded during the survey of 2002-2012 and an additional 39 species were detected during 2015-2016. Twenty species recorded during 2002-2012 were not found during 2015-2016 surveys. In addition, the bird checklists of Adhikari et al. (2000Adhikari et al. ( , 2018 included 12 and 6 bird species, respectively, which were not recorded during our survey (2002-2012 and 2015-16) in Barandabhar. In November 2019, Great White Pelicans Pelecanus onocrotalus were spotted in BCF (Kathmandu Post 2019) which is also included in our checklist. Accipitridae family consisted of the highest number to cover all habitat types (wetlands, grasslands, open areas, forest) of BCF. At each starting point and at every 250 m throughout the transect, there was a minute disturbance pause and five-minute observation pause to sight the birds. Bushnell binoculars (8 x 42) were used to sight the birds. Every year, pre-monsoon (March-April) and post-monsoon (October-November) surveys were conducted to detect the summer and winter visitors, respectively. Since the activities of the birds are high in the morning period, we chose the survey time from 0700 to 0900 h. Only one transect was surveyed each day to limit the research in the morning (0700-0900 h). For long transects (>4 km), we either mobilized multiple groups of the surveyors (3-4 surveyors/group on foot) or the same team surveyed on multiple days depending on the length of the transect. For example, an 11-km transect was surveyed in three days (average 4 km transect survey in a day in two hours survey period). The survey in a transect was continued the next day from the point it was left in the previous day. The total number of bird species encountered was recorded in this period. We also collated the bird checklist previously published

J TT
of species (n= 32) followed by Muscicapidae (n= 30), and Anatidae (n= 18). According to the foraging guild, insectivorous bird species were highest (n= 180 species) followed by equal number of carnivorous (n= 41) and omnivorous (n= 41) species ( Figure 2). Out of the total bird species recorded, 62.9%, 26.6%, 7.5%, and 2.9% of bird species of BCF are resident (R), winter migrants (W), summer migrants (S), and passage migrants (P), respectively (Table 1). The bird list also includes globally threatened species: five Critically Endangered, three Endangered, eight Vulnerable, and 15 Near Threatened species. In CITES enlisted categories, we recorded a single bird species each in CITES I and CITES III, and 53 bird species in CITES II category. According to the habitat type, there were 181 bird species of forest, 74 species of wetland, 24 species of grassland, 70 species of open field, and 23 species of partially wetland birds ( Figure 3). The checklist is presented in Annexe 1.

DISCUSSION
Our study reported a high diversity of bird species in Barandabhar including 16 globally threatened species (Critically Endangered, Endangered, and Vulnerable) which further justifies the stronghold of its IBA status. The proximity to Chitwan National Park, one of the global biodiversity hotspots may have contributed to the high species diversity of birds. The southern portion (south of the highway of BCF) is the buffer zone of CNP and includes the Ramsar listed Beeshazar and associated lakes. CNP has a total of 544 recorded bird species (CNP 2019). As a contiguous habitat, the movement of the birds from CNP to adjoining BCF area is obvious.
Insectivorous bird species are dominant amongst the various species in BCF consisting of 48.38% of the total species. A recent study suggests that 40% of the insect species globally are in decline due to intensification of agriculture using a large volume of pesticides and fertilizers (Hallmann et al. 2017;Dougals 2019). Schrauth & Wink (2018) stated that the decrease in insect abundance affects higher trophic levels like insectivorous birds. There is no cultivation inside BCF and human movements are also limited. We do not have data on the insect communities of BCF. However, we can hypothesize that the high number of insectivorous bird species in BCF means good insect communities are likely to be thriving in the area. Besides the insectivores, the carnivore and omnivore are the second largest group by species diversity (11% each) in BCF.
A total of nine scavenger species was recorded from BCF, of which four are Critically Endangered, and among them three are resident. BCF is immediately surrounded by municipalities with agricultural fields and pasture for livestock. The scavengers are dependent on dead wildlife/ livestock in and around BCF. The use of diclofenac is detrimental to the survival of these scavengers (Oaks et al. 2004;Swan et al. 2006). So, a conservation awareness program to communities on the use of meloxicam which is an alternative for diclofenac would be a good solution for the survival of a viable population of scavengers (Swarup et al. 2007;Thapa 2009) BCF supports 62.9% resident, 26.6% winter migratory, 7.5% summer migratory, and 2.9% passage migrant birds. These migratory species have different breeding sites, wintering sites, and stopover sites or passage routes. These are sensitive species because a disturbance in any of these sites can cause a decline in their population. Since, BCF is a small biological corridor for migratory and passage birds, we must focus on to return the healthy breeding population so that they visit the area every year.
The transect used for the 2015-2016 surveys seems more effective because 10% more species were recorded in these two years compared to 2002-2012. Even so, the data lack the total species present in the survey of 2002-2012. This may be because the survey efforts of 2015-2016 covered 384 km compared to the survey efforts of 1,122 km during the 2002-2012 surveys.
One of the major challenges of the 21 st century is to globally reduce the rate of species loss (Barnosky et al. 2011;Pimm et al. 2014;Rosenberg 2019). In order to reduce threats to existing bird diversity in BCF, the government has endorsed the Barandabhar Corridor Forest Management Plan and the Beeshazari Lake Management Plan that aim to conserve the flora and fauna and their habitat in BCF. The proper implementation and timely revision of these existing